Various types of emergency shutoff systems have been proposed, including the system disclosed in U.S. Pat. No. 7,036,441. The system disclosed in the '441 patent allows an operator to close off a line in the event of a leak, and automatically shuts the system down in the event of a nurse tank breakaway. Manual valve closure is thus permitted by the operator.
The prior art also includes valves with a “cam over in line” feature, as embodied in the Fisher Model C 407-10 internal valve. An excess flow feature of the valve enhances the unreliability of excess flow shutoff valves, so that the valve closes in response to a leak condition. One problem with this valve design is that errors in piping the system may result in “leaks” of varying magnitude that may undesirably result in closing the excess flow valve.
The disadvantages of the prior art are overcome by the present invention, and an improved emergency shutoff system and method are hereinafter disclosed.